Hydraulic movement transmitting system



Aprig 1946. E. R. ROBERTSON 2,399,296

HYDRAULICv MOVEMENT TRANSMITTING SYSTEM Filed July 15, 1944 2Shqecs-Sheet 1 g 4 I) s INVENTOR EDWARD ROKER ROBERTSQN ATTORNEY S Ap i30, 19 6 E. R. ROBERTSON sm HYDRAULIC MOVEMENT TRANSMITTING SYSTEM FiledJuly 15, 1944 2 Sheets-Sheet 2 r I ma.

MM K QM,OMM4Z-ML Patented Apr. 30, 1946 HYDRAULIC MOVEMENT. TRANSMITTINGSYSTEM Edward Roker Robertson, Middlescx, England, assignor to SimmondsAerocessories Limited; London, England Application July 15, 1944, SerialNo. 545,149 In Great Britain July 23, 1943 7 operation of the spring itwill still vary with Claims.

This invention relates to hydraulic movement transmitting or telecontrolsystems which comprise a transmitter having two or more compressibleliquid holding chambers, of the "Sylphon bellows type, connectedrespectively with pipe lines and a receiver having two or moreexpansible liquid holding chambers connected with the pipe lines suchthat compression of a transmitting chamber causes an expansion of acorresponding receiving chamber.

In systems of the above kind it is necessary to provide compensatingmeans which permit of the expansion and contraction of the workingfluid, due to changes in temperature, without aiiecting the operation ofthe system as a whole. In one known arrangement such means compriseauxiliary Sylphons, one for each pipe line, the movable ends of whichare connected together such that whil an increase in pressure in all thepipe lines will cause the Sylphons to expand an increase in pressure inone pipe line and a reduction in pressure in another line, such asoccurs during transmission of movement, will have no efiect. One exampleof a system of this kind is shown in U. S. Patent No. 2,168,397.Alternatively the Sylphons at the transmitter or at the receiver maythemselves operate to provide the desired compensation. One example ofthis arrangement is shown in U. S. Patent No. 1,791,489 in which in atransmitter comprising two Sylphons the free ends of the "Sylphons areconnected to opposite ends of a pivoted link and the motion to betransmitted is applied to the pivot. Thus expansion of the fluid merelycauses both "Sylphons to expand and rotate the link about its pivotwhile movement of the pivot causes one Sylphon to expand and the otherSylphon to contract.

In these known hydraulic systems it has been found that if the staticpressure of the operating liquid is low a sudden movement of thetransmitter may reduce the pressure in one of the pipelines to asubatmospheric pressure when the liquid column inthe pipe will break,thus putting the system out of action. Moreover the static pressure inthe system, being due solely to the spring of the Sylphons, may fall toa very low value as the liquid and the "Sylphons contract at lowtemperatures. It has accordingly been proposed in my prior Britishspecification No. 543,340 to provide a spring which causes the "Sy1phonsof a system of the kind described in U. S. Patent No. 1,791,489 to beurged towards their compressed positions. In this arrangement althoughthe static pressure is increased by the expansion or contraction of theoperating liquid and at low temperatures may fall to a value such thatoperation of the system produces a subatmospheric pressure or vacuumsufiicient to break the liquid column. Moreover in this arrangement ifthe static pressure he raised to a suitable level at the lowest workingtemperature by the use of a suitable spring the pressure may increaseabove a safe value at the highest working temperature.

It is accordingly an object of the present invention to provide anhydraulic system in which the static pressure is maintained at asuitable level over the Whole working temperature range.

A further object of the present invention is to provide an hydraulicsystem of the kind described in which the static pressure is maintainedsubstantially constant at any temperature with in the working range.

Other objects and advantages of the present invention will becomeapparent during the course of the following description with referenceto the accompanying drawings in which- Fig. l is a plan view of areceiver embodying the invention, and Fig. 2 is a central verticalsection on the lines 22 of Fig. 1 looking in the direction of thearrows, certain of the elements shown in Fig. 2 not being shown in Fig.1.

While the receiver illustrated forms part of a system of the kinddescribed in U. S. Patent No. 2,168,397, that is of the kind in whichadditional "Sylphons are provided for temperature compensation it willbe appreciated that the invention may also be applied to systems of thekind shown in U. S. Patent No. 1,791,489 in which the Sylphons at thetransmitter or at the receiver; also act as compensating devices.

The receiver shown in Figs. 1 and 2 comprises a base casting l0 havingthereon upstanding apertured lugs H and I2 to which the heads of Sylphontype bellows I3 and I 4 are secured by nuts Hi. The bellows areconnected to pipe lines I! and I8 which extend through a flexiblemetallic tubing l9 to a transmitting device. The movable heads ofbellows I 3 and I 4 are connected together by means of a link 20, thecentre of which is pivotally connected with a member 2! by means of apin 22. The lower end of member 2| is pivotally mounted on a fixed pin23 and the upper end is provided with an arcuate rack z l having teethengaging with a pinion 25 mounted on spindle 26. A pointer 21 (Fig. 2)movable over a fixed scale 28 is secured to one end of the spindle 26.Backlash between the teeth of rack 24 and pinion 25 is prevented by acord 29, one end or which is wrapped around the spindle 26. The otherend or the cord is secured to the free end of a V-shaped spring 30, theother end of which is anchoredto a pillar 36 on the base casting Ill.

The temperature compensating device comprises a pair of 'Sylphon typebellows 3| and 32 mounted on lugs 33 and 34 by means of nuts 35. Themovable heads of these sylphons are connected by arms 31 and 38 withopposite ends of a link 39 pivotally mounted on a fixed pin 40. Theupper end of link 39 is provided with an extension 4| on which ismounted a pin 42 and a spring 43 extends between this pin and a pillar44 mounted on the base casting Hi. The compensating bellows 3| and 32are connected with the working bellows l3 and I4 and with the pipe linesl1 and H! by means of pipes 45 and 46 respectively.

The operation of the system is as follows- Pressure differencesoccurring in the pipe lines I! and I8 due to the operation of thetransmitter will cause bellows l3 to expand and bellows M to contract orvice versa. Such movement of the sylphons will cause the rack 24 to moveto produce a corresponding movement of the pointer 21. Such pressuredifferences will, however, be unable to cause movement of thecompensating bellows 3| and 32; since the spring 43, which urges boththese bellows to a compressed position is sufficiently strong to preventsuch movement for any pressure produced in the system under normalworking conditions. The bellows are, however, free to expand togetheragainst the action of the spring 43 as the volume of liquid in thesystem increases due to an increase of the ambient temperature.

As shown in Fig. 1 the compensating bellows 3| and 32 are in theposition they .occupy at a mean working temperature, and the spring 43exerts a torque on the link 39 about pin 40 to urge the bellows to theircompressed position. As the working temperature increases and thebellows expand inwards the torque exerted by the spring 43 decreasessince the perpendicular distance between the axis of the spring and thecentre of pivot pin Ml decreases. Also the torque sorted by the springwill increase as the temperature falls. Thus the varying torque exertedby the spring supplements the efiects due to the spring rate of thebellows themselves which in the absence of the spring produce a maximumstatic pressure in the system at the maximum working temperature and anundesirably low minimum static pressure at the minimum temperature. Bysuitably balancing the effects of the spring in relation to the springrate of the bellows the static pressure in the system, over a desiredtemperature range, may bemaintained substantially constant and, ifdesired, at a relatively high value, e. g., 100 lbs. [1 such that theinstantaneous pressures developed during reasonable operation of thesystem can never at any sating for volumetric changes of the workingfluid comprising a bellows connected with each transmission line, meansfor maintaining the static fluid pressure in the line substantiallyconstant comprising alink pivotally connected between a free end of saidbellows and a fixed point, a spring connected under tension between apoint on said linkand a second fixed point, the arrangementof the springbeing such that the spring exerts a torque on the link which increasesas said bellows contracts.

2. In an hydraulic motion transmitting system of the kind specifiedhaving a pair of pipe lines connecting transmitter and receiver and atemperature compensating device comprising a pair of bellows connectedone with each pipe line, the free ends of the said bellows beingconnected with opposite ends of a centrally pivoted link, and a springunder tension connected between one end of said link and a point fixedrelative to the pivot of saidlink and so positioned that the axis of thespring moves away from the axis of the pivot of the link as the bellowscontract.

3. An hydraulic movement transmitting system as claimed in claim 2wherein the axis of the spring and the axis of the pivot intersect whenthe bellows are fully expanded.

4. In an hydraulic movement transmitting system of the kind specifiedhaving a pair of bellows the free ends of which are connected withoppo-' site ends of a centrally pivoted link such that the bellows arefree to expand or contract together. to compensate for changes in volumeof 440 the working fluid, means for maintaining the static pressure ofthe fluid substantially constant comprising means for applying a forceto said bellows which urge them toward their contracted position, saidlast-mentioned means being so arranged with respect to the pivot of saidlink thatthe force applied to said bellows increases in magnitude as thebellows contract.

5. In an hydraulic movement transmitting system of the kind specifiedhaving a pair of bellows the free ends of which are connected onopposite sides of the pivot of a centrally pivoted link, the bellows andlink being arranged in such a manner that the bellows are free to expandor contract together to compensate for changes in volume of the workingfluid in the system, means for applying a force to said pair of bellowstendingto move the free ends thereof to a contracted position, saidmeans comprising a spring under tension connected between'one end ofsaid pivoted link and a point fixed with reference to the pivot of saidlink and offset relative to the axis of the said link.

EDWARD ROKER ROBERTSON.

